1. Field of the Invention
The present invention relates to an image display device by which an optical image signal based on image information is projected onto a display means to display an image, and a method for adjusting optical elements of in the image display device into alignment.
2. Description of the Prior Art
FIG. 95 is a diagrammatic representation of a conventional image display device. Reference numeral 1 denotes a luminous element for emitting light; 2 denotes a parabolic reflector for reflecting the light from the luminous element 1 mostly into parallel rays of light; and 3 denotes a condenser lens for gathering the light reflected by the parabolic reflector 2. The luminous element 1, the parabolic reflector 2 and the condenser lens 3 constitute an illumination light source system.
Reference numeral 4 denotes a light valve for spatially intensity-modulating the light gathered by condenser lens 3 based on image information; 5 denotes a projecting optical lens for projecting the light intensity-modulated by the light valve onto a screen; and 6 denotes the screen for displaying, as an image, the light projected thereon by the projecting optical lens 5. The arrows indicate optical paths.
Next, the operation of the prior art example will be described below.
Light emitted from the luminous element 1 is reflected by the parabolic reflector 2 and focused through the condenser lens 3 onto the light valve 4. The light valve 4 spatially intensity-modulates the focused light based on image information. The intensity-modulated light is projected by the projecting optical lens 5 onto the screen 6 from behind (from the left-hand side in FIG. 95) and displayed thereon. A user of the image display device visually identifies the image from the front (from the right-hand side in FIG. 95).
The depth dimension of the image display device of FIG. 95 corresponds to the distance from the illumination light source system composed of the luminous element 1, the parabolic reflector 2 and the condenser lens 3 to the screen 6. It is preferable to minimize the depth dimension of the image display device if the image size displayable is the same. For such a reason, the conventional image display device of FIG. 95 uses a wide-angle projecting optical lens 5 to display an image on the screen so that the depth dimension of the display device is minimized to provide a flat device configuration.
Since the projecting optical lens 5 has a limitation of increasing its angle of field, however, it is customary in the art, with a view to reducing the depth dimension, to place a plane mirror at an angle of 45° to the horizontal to bend the optical path from the projecting optical lens 5, projecting an image onto the screen 6 as depicted in FIG. 96.
In the image display device of FIG. 96, the illumination light source system, the light valve 4 and the projecting optical lens 5 are disposed in the direction of height of the device (in the vertical direction in FIG. 96) to reduce the depth dimension of the device. The depth dimension of the image display device in this case corresponds to the distance from the plane mirror 7 to the screen 6. With the plane mirror 7 tilted more than 45° from the horizon, the depth dimension of the image display device can be further reduced; in this instance, however, the light valve 4 and the illumination light source system interfere with the projected light, and the light is shaded or eclipsed accordingly, resulting in the light path getting out of the screen 6.
In Japanese Patent Application Laid-Open Gazette 6-11767 there is disclosed an image display device of the type wherein light is reflected by a convex mirror is used in place of the plane mirror 7 in FIG. 96 to display a magnified image on the screen 6, but the image displayed on the screen 6 is distorted.
The conventional device configurations described above impose limitations on the reduction of the depth dimension of the device and permit no further reduction.